Method and apparatus for growing free oyster spat



United States Patent Inventors Appl. No.

Filed Patented Assignee William W. Budge Hillsborough, California;

George Walter Freeborn, Woodside, California Nov. 30, 1967 Sept. 1, 1970Pacific Maricuiture, Inc.

Pescadero, California a corporation of California METHOD AND APPARATUSFOR GROWING FREE OYSTER SPAT 21 Claims, 5 Drawing Figs.

U.S.Cl

Int.Cl

..... A01k6l/00 [50] Field ofSearch 1 19/4, 2

[56] References Cited UNITED STATES PATENTS 463,397 11/1891 Walton, Sr119/4 1,660,259 2/1928 Elsworth 119/4 2,302,336 11/1942 Macdonald..119/2 3,196,833 7/1965 Glancy 119/4 3,316,881 5/1967 Fischer 119/4Primary Examiner-Hugh R. Chamblee Attorney- Flehr, Hohbach. Test,Alhritton and Herbert ABSTRACT: Method and apparatus for growing freeoyster spat by removing the spat from the cultch within a period lessthan thirty days after adherence to the cultch, and thereafter growingthe spat free ofa cultch.

Patented Sept. 1, 1970 F i g. 2

INVENTOR. William W Budge e W Fr eborn METHOD AND APPARATUS FOR GROWINGFREE OYSTER SPAT BACKGROUND OF THE INVENTION This invention relates tothe growing of oyster spat and more particularly to the growing of freeoyster spat.

Heretofore in the growing of oyster spat, it has been necessary toprovide cultch material for the oyster larvae to set upon when it passedthrough metamorphosis. Many different types of cultch material have beenutilized, such as cleaned oyster shells. Other materials have also beenused such as tile and plastic rope. When utilizing such cultchmaterials, it often has been the practice to let the oysters grow tomaturity on the cultch and then to harvest them. In all cases, it hasbeen thought necessary to leave the oyster spat on the cultch materialuntil the oyster spat had attained an age ranging from 6 to 12 monthsand which had a size ranging from 1 inch to 2- -3 inches. This had beenthought to be necessary so that the oysters would be sufficientlydurable to withstand removal from the cultch material and to survivefree of the cultch material.

The utilization of such cultch materials for the growing of spat hasposed many problems for commercial oyster hatcheries. For example, it isnecessary to acquire large quantities of the cultch material which, ifit is oyster shell, must be properly cleaned and then drilled with holesso that it can be placed on strings to permit handling of the same ingroups. After the larvae have set upon the cultch material, it isnecessary to grow the oyster spat on the cultch material so it has anage ranging from 6 weeks to IO weeks and has a size ranging from 3millimeters to l centimeter so that it can be shipped to an oystergrower. In the past, it has been necessary for the oyster grower totransport the spat secured to the cultch material and to further growthe spat until it reaches an age ranging from 6 to 12 months and havinga size ranging from I inch to 23 inches so that the grower could removethe same from the cultch material and plant the oysters in oyster beds.From the foregoing, it can be seen that there is a considerable expensein the handling and transportation of the cultch material which addssubstantially to the cost of growing oysters. There is, therefore, aneed for a new and improved method and apparatus for growing of oysterspat.

SUMMARY OF THE INVENTION AND OBJECTS The method for growing free oysterspat comprises growing oyster larvae in a free swimming state in avessel, causing oyster larvae to set upon a relatively smooth surfacewhen the larvae pass through metamorphosis to become oyster spat. Theoyster spat is removed from the surface to which it has adhered within aperiod of less than thirty days from when it has set on the surface, andpreferably when the oysters have a size which is less than onecentimeter.

In general, it is an object of the present invention to provide a methodand apparatus for growing free oyster spat which permits the oyster spatto be removed within thirty days after the oyster has set on a surfaceand when it has a size less than one centimeter.

Another object of the invention is to provide a method of the abovecharacter which makes it possible to ship spat very inexpensively andover long distances.

Additional objects and features of the invention will appear from thefollowing description in conjunction with the preferred embodiment ofthe invention in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a tubutilized for growing oyster larvae.

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is an isometric view ofa large tank with trays therein for thegrowing of spat.

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3.

FIG. 5 is a cross-sectional view taken along the line 55 of FIG. 4.

DESCRIPTION OF PREFERRED METHOD AND APPARATUS In practicing the presentmethod for the growing of free oyster spat, the oyster larvae isproduced by techniques which are conventional in commercial oysterhatcheries. In ac- 0 cordance with such conventional practices, male andfemale oysters are induced to spawn by immersing them in warm sea waterranging in temperature from 20 to 32C. The eggs discharged rangetypically from 45 to 60 microns with the majority measuring between 50and 55 microns. The fertilized eggs are kept in sea water having atemperature approximately 25C. and as cleavage progresses, the embryogradually develops into a swimming ciliated larva and reaches thetrochophore stage within 12 to 16 hours. Late in the trochophore stage,the shell gland begins to secrete the shell and when the shellcompletely encloses the soft parts, the larva has reached the earlystraight-hinge stage. This also may be called the shelled-veliger stage.The smallest normal straight-hinge larvae measure approximately 68 x 55microns. Within 48 hours, at a temperature of approximately 25C. in seawater, the larvae measure approximately 75 x 67 microns. At this stage,they begin to take in particulate food.

The larvae are highly active and remain in suspension in the sea waterthroughout the free swimming period. The larvae metamorphose when theyare between 275 and 315 microns in length, but occasionally freeswimming larvae may be of a greater size. The larvae are normally grownto metamorphoses in sea water at temperatures ranging from approximately17 to 33C.

In accordance with the present invention, the larvae are grown in seawater in plastic tubs 11 formed of polyethylene in which sea water 12 ismaintained at the desired temperature of approximately 25C. by the useof thermostatically controlled electrical immersion heaters 13. The seawater in the tubs 11 is aerated with air through a tube 14 extendingdownwardly, into the sea water and supported from a support member 16.

Prior to the time the larvae reach metamorphoses, sheets 21 of amaterial, which can be bent but which will retain its shape, are placedin the sea water to provide surfaces to which the oyster larvae canattach at the end of the free swimming stage to become the oyster seedor spat 22. One material found to be particularly suitable is lead. Byway of example, thin sheets of lead approximately 3 inches wide, 9inches long, and approximately 1/32 inch in thickness were utilized. Itis desirable that the material have a relatively smooth surface so thatthe oyster spat can be removed readily as hereinafter described.

It has been found that the oyster larvae have a great affinity for thelead and readily set on the lead sheets. Other materials have been triedwith less success. For example, polyethylene, polyvinyl, chloride,Teflon and nylon sheets have been tried. The oyster larvae do set onthese sheets but not as readily. However, it has been found that ifpolyethylene sheets are aged for several years in sodium hypochloriteto, in effect, provide slightly roughened surfaces, the polyethylenesheets do provide a relatively attractive surface for the larvae andwill interest the larvae in setting on the same. Pewter and silversheets have also been tried with a lesser degree of success. Othermaterials could be utilized; however, they have disadvantages. Forexample, iron has a tendency to corrode which causes discoloration ofthe water and is harmful to the oyster larvae. Galvanized steel has alsobeen found to be harmful to young oyster spat.

In general, in accordance with the present invention, it has been founddesirable to provide surfaces which are relatively smooth to which theoyster larvae can attach when they are setting. The use of separatesheets 21 of material placed within the tubs 11 has the advantage inthat the sheets can be readily removed for removal of the spat ashereinafter described. In practice, it has been found that the spat hasa tendency to set on the underside of the bent sheet as indicatedparticularly in FIG. 1 of the drawings. In order to encourage the larvaeto also set on the other side of the sheet of material, it has beenfound that after larvae have first set on one side, the sheet ofmaterial can be removed and then bent so that the other side is concaveand then again replaced within the tub. It has been found that thelarvae then will readily set on the other side of the sheet. It also hasbeen found that at the time the larvae is setting on the sheets 21within the tub, substantial quantities of the larvae will actually seton the tub itself and principally upon the inner side of the bottom wallof the tub although a few larvae will even set upon the inner surfacesof the side walls ofthe tub.

The larvae grown in the tub are generally of the same age and also willpass through metamorphosis and set within a twenty-four hour period andcertainly within a forty-eight hour period.

The spat are removed from the surfaces on which they have set after thespat have had an opportunity to grow after being set for a period of atleast twelve hours and preferably for a period of at least twenty-fourhours. The spat should not be allowed to remain set for a period greaterthan thirty days before removal because thereafter removal is verydifficult and may destroy the oyster. The spat, upon removal, have asize which is preferably from 300 to 500 microns and less than onecentimeter in the major dimension. In practice, we have found itdesirable to remove the oyster spat from the sheets of material withinone to five days and having a size ranging from 300 to 500 microns. ithas been found to be possible to produce free live spat with almost 100percent survival by removing the oyster spat from the surface to whichit has adhered after it has been set for twenty-four hours and in whichthe individual oyster seed has a size of approximately 300 microns.

Several methods have been utilized to remove the oyster spat inaccordance with the present invention without damaging substantialquantities of the oyster spat. One method which has been found to beparticularly desirable is to utilize a brush having soft bristles andbrushing the oyster spat into specially prepared trays 26. For example,when a lead sheet is used, the oyster spat can be first brushed off oneside of the sheet, and then the sheet can be bent in the oppositedirection and the oyster spat removed by brushing the other side.

The oyster spat can be removed from the side walls of the tub 11 andalso from the bottom wall ofthe tub by the use ofa brush after the seawater 12 has been removed from the tub.

It also has been found that it is possible to remove the oyster spat byutilizing a very small jet of water under high pressure and bending thesheet as the jet ofwater is applied to the sheet to cause the oysterspat to be removed therefrom.

By providing the oyster larvae with a surface which is relativelysmooth, it is difticult for the oyster to adhere too strongly to thesheet of material and, therefore, it is relatively easy to remove theoyster without damaging the oyster. Also, because of this fact, it ispossible to use a soft rag or a sponge to remove the small oysters fromthe sheets of material.

Upon removal ofthe oyster spat from the sheets of material, the oysterspat are put back into tubs of sea water and are grown under conditionswhich would favor the growth of larvae. Since the spat are heavier thansea water and no longer have means of propulsion they sink to the bottomof the tub. At least once a day the spat lying in the bottom ofthe tubare moved about with a soft brush. This discourages reattachment of thespat. The spat are grown in this manner for several days until they willnot pass through a screen which has square openings which areapproximately 370 microns on a side. Spat that are defective or whichwere damaged in removal from the sheet surface will never attain thesize required to hold on this screen and are thus eliminated from thebatch.

When the spat attain sufficient size to hold on the 370 micron screenthey are removed from the tubs and placed upon a very fine mesh screen27 which forms the bottom wall of the tray 26. The screen has openingswhich are only slightly less in size than the size of the oyster spat.Thus, it has been desirable to provide a fine mesh screen which hassquare openings which are approximately 333 microns in size. The screenis preferably formed ofa material for which the oyster does not have aparticular affinity to thereby discourage the oysters from setting onthe screen. One material found particularly satisfactory is a fine nylonmesh screen. The screen 27 is secured to the bottom sides of arectangular wooden framework 28 formed by a pair of spaced parallel endmembers 29 and a pair of spaced parallel side members 31 which arefastened together in a conventional manner. The tray has a depth ofapproximately six inches and a width of approximately 24 inches and alength of 36 inches.

As soon as a sufficient quantity of oyster spat has been placed in thetray, the tray is immediately placed in a large tank 36 carrying seawater 37 which is retained at the desired temperature, as for example25C., for growing oysters. The trays are floated on top of the sea waterand the weight of the tray itself is sufficient to cause the screen 27carried by the tray to be disposed below the surface of the water by asuitable distance, as for example one-half inch, so that the oyster spatcarried on the top surface of the screen are disposed below the surfaceof the sea water as shown particularly in FIGS. 4 and 5.

Means is provided for cleaning the trays during the time the oyster spatare growing therein and also for providing food to the young oysters inthe trays and consists of a piping system 40 formed of a suitablematerial, such as plastic, which includes a circular pipe 41 whichextends around the circumference of the tank 36 and is secured to thetop edge thereof. The pipe 41 is provided with a plurality of T5 42which are connected to lines 43. Lines 43 are connected to T5 44(F1G.4). T5 44 are connected to laterals 46 which feed into elbows 47connected to a pair of spaced parallel feeder lines 48 that extendlongitudinally of the tray 26 and overlies the tray. The ends of thefeeder lines are closed by caps 49. The feeder lines 48 are providedwith a plurality of longitudinally small holes 51 in the bottom sides ofthe line to permit the sea water carried by the piping 41 to rain downupon the oyster spat within the trays 26.

The sea water supply to the piping system 40 is supplied through a motordriven pump 53 which is connected to a pipe 54 that leads to a heater(not shown), and a filter (not shown) for treating the water which iswithdrawn from a line 56 at the bottom of the tank 36 for recirculation.Means (not shown) is also provided for periodically introducing food ofthe type required by the oyster spat into the sea water in piping 40before it is supplied to the pump 53.

It has been found that raining the sea water down upon the oyster larvaewithin the trays 26 is particularly beneficial. It has been found thatraining the water down upon the screen flushes the detritus and otherwaste material away from the animals or oysters and keeps the oysterspat free and clear of any foreign material to provide the best possibleenvironment for the growth of the oyster spat. The water which is raineddown upon the oyster spat is maintained at the desired temperature forgrowing of the oyster spat, as for example 25 C. The materials which areflushed through the trays go to the bottom of the tank 36 and are movedfrom the tank and filtered therefrom before the recirculated water isagain rained down upon the spat.

The small mesh screen which is provided in trays 26 as the water rainsdown upon the same provides an excellent environment for the growth ofthe spat and at the same time discourages the spat from re-attachingthemselves. Because the screen is provided, there is much lesslikelihood of the spat re-attaching to the screen. Re-attachment is alsodiscouraged by motion caused by the sea water raining down upon thespat.

The spat is grown to the desired size within the trays 26. Preferably,the growers who grow oysters wish to receive the oysters at a size whichis greater than 6 mm, for example 8- 15 mm. With the present method,oyster spat can be grown to this size within one to two months. ifdesired, the oysters can be grown to a larger size, as for example 3 em,if desired, by the grower.

in growing young oysters to larger sizes, it may be desirable to usetrays such as trays 26 having a screen with larger openings therein. Forexample, at an intermediate stage when the oysters are larger than 2mm., it would be desirable to remove the spat from the trays 26 shown inFIGS. 4 and 5 and to provide trays having screens with the larger mesh.This is desirable because it provides less surface for the oysters toreattach themselves and encourages the oysters to remain free so thatthey can be readily removed from the trays and shipped to the growers.

By the use of the foregoing method and apparatus, it has been possibleto provide free growing oysters at a very early age which heretofore wasthought to be impossible. Since the oysters are free growing, they arerelatively easy to ship because there is no necessity to provide cultchmaterial or to ship cultch material with the oysters. This makes itfeasible to transport spat by air throughout the United States ofAmerica and, in fact, throughout the world from a single location.

It has been found that free oyster spat prepared in the manner describedabove is as capable of adapting to the environments in whlch it isplaced to grow into mature oysters as the spat which has previously beengrown on cultch material. In addition, it has been found that the spatwhich is grown with the present method is more desirable because thespat is removed from the surface to which it has attached while veryyoung. For this reason, the spat is all of substantially uniform sizeand has not modified its shape in order to conform to the cultchmaterial on which it normally grows. Also, it has not been distorted bygrowth of neighboring spat growing on the same piece of cultch material.Thus, by use of the free oyster spat, it is possible to provide a moreuniform and more desirable commercial oyster.

lt is apparent from the foregoing that there has been provided a new andimproved method and apparatus for the growing of oyster spat which hasvery significant commercial aspects particularly in that it now makespossible the shipping of oyster spat by air to remote locations atrelatively low cost. The method and apparatus also makes it possible togrow the oysters more rapidly so that they can be shipped to growerswithin a shorter period of time.

We claim:

1. In a method for growing oyster spat, growing oyster larvae in a freeswimming state in a container having therein a body of water which is incontact solely with said container and a cultch material, said cultchmaterial having only relatively smooth surfaces for which oyster larvaewill have an affinity when they pass through metamorphosis, permittingthe oyster larvae to set primarily on said cultch material having arelatively smooth surface as the oyster larvae pass throughmetamorphosis to become oyster spat, and removing substantially all theoyster spat from the relatively smooth surface of the cultch materialafter the oyster spat has set for a time which is less than thirty days.

2. A method as in claim 1 wherein the oyster spat is removed in a periodranging from 1 to 5 days after it has set and having a size ranging from300 microns to 5 millimeters.

3. A method as in claim 1 wherein the cultch material includes sheets offlexible material disposed in the body of water.

4. A method as in claim 1 wherein the oyster spat is removed by the useof a stream of water impinging upon the surface ofthe cultch material.

5. A method as in claim 3 wherein the sheets of cultch material areflexed to facilitate removal of the spat.

6. A method as in claim 1 wherein the cultch material includes sheetsoflead.

7. A method as in claim 1 wherein said oyster spat is removed when ithas a size which is less than 2 millimeters.

8. A method as in claim 1 wherein said oyster spat is removed when ithas a size ranging from 300 microns to one centimeter.

9. A method as in claim 1 together with the step of placing the oysterspat on a relatively fine mesh screen and raining sea water down uponthe oyster spat while it is on the screen.

10. A method as in claim 9 wherein the screen forms the bottom wall of atray having upwardly extending side walls together with the step ofpositioning the tray in a tank of water so that the screen is below thesurface of the water and the spat is covered by the water in the tankand the upper extremities of the tray are above the surface of the waterto prevent the loss of the oyster spat from the tray.

11. A method as in claim 9 together with the step of supplying food tothe oyster spat by supplying it in the water being rained down upon thespat.

12. A method as in claim 9 wherein the screen which has a mesh in whichthe openings therein are only slightly smaller than the size of theoyster spat to discourage the oyster spat from adhering to the screen.

13. In apparatus for growing oyster spat, a tub formed of material whichis resistant to attack by sea water, a quantity of sea water disposed inthe tub, means for retaining the sea water at a predeterminedtemperature, said tub being free of any material which does not have arelatively smooth surface and being formed of a material having arelatively smooth inner surface and a removable cultch material withinsaid tub having only relatively smooth surfaces which will attract thesetting of oyster larvae thereon.

14. Apparatus as in claim 13 wherein said cultch material ispolyethylene.

15. Apparatus as in claim 13 wherein said cultch material is a metalwhich can be bent and will retain its shape within the sea water.

16. Apparatus as in claim 15 wherein said cultch material is lead. 7

l7. Iii an apparatus for growing oyster spat, a tank formed of materialresistant to attack by sea water, a quantity of sea water within thetank, at least one tray disposed in the tank, said tray being formed ofa framework which floats in the water and having an open top side and anopen bottom bottom side, a fine mesh screen carried by said frameworkand covering said bottom side of the framework, said tray being free ofcultch material and being positioned in the sea water so that its openside faces upwardly with the screen being immersed in the water at alevel which is below the surface of the water so that oyster spatcarried on the screen are disposed below the surface of the water andwith the framework extending above the surface of the water to retainthe oyster spat on the screen.

18. Apparatus as in claim 17 together with means for raining water downupon the screen.

19. Apparatus as in claim 18 wherein said means for raining water downupon the screen comprises plastic piping having a plurality of openingstherein, said plastic piping overlying the tray and resting upon thetray.

20. Apparatus as in claim 17 wherein a plurality of trays are floatingwithin said tank and wherein said piping includes means for raining downsea water on the screens of each of said trays.

21. In a method for growing oyster spat, growing oyster larvae in a freeswimming state in a container having a body of water in contact solelywith said container and a cultch material, said cultch material havingonly relatively smooth surfaces for which oyster larvae will have anafiinity when they pass through metamorphosis, permitting said oysterlarvae to remain in said body of water until the oyster larvae passthrough metamorphosis to thereby permit the oyster larvae to set uponsaid relatively smooth surfaces of said cultch material to become oysterspat, removing substantially all of the oyster spat from the surfaces ofsaid cultch material within a period of time which is less than thirtydays after the oyster spat has set, and placing the removed oyster spatin a separate body of water in an environment in which the oyster spatwill be separate from each other so that they can be shifted independentof each other to permit their ready shipment to other locations.

